Rotation transmission devices are known which comprise a flexible shaft and a sheath inside which the shaft is housed. In these transmission devices, in particular for adjusting seats for motor vehicles, the speeds of rotation of the shaft in the sheath are greater than 2000 revolutions/minute, conventionally around 3000 revolutions/minute. To allow rotation at such speeds, a clearance of a few tenths of a millimeter is necessary between the shaft and the sheath. However, this clearance gives rise, during the rotation, to the appearance of low-amplitude vibrations which propagate along the shaft and cause an unpleasant noise and sensation to the touch.
To resolve this problem of vibration, the document JP 07 310 730 proposes a rotation transmission device whose sheath has at least one deformation in the form of a constriction, that is to say a local reduction in the diameter of the sheath. This is because this constriction, by causing gripping contact between the shaft and the sheath, limits the vibrations. However, this contact creates significant rubbing between the shaft and the sheath, which makes it necessary to increase the motor torque in order to obtain a sufficient speed of rotation of the shaft for the application envisaged. In addition, this friction causes premature wear on the sheath at the deformation.
The invention aims to mitigate these drawbacks by proposing a device for transmitting a rotation movement whose sheath has permanent deformations which are arranged so as to limit the vibrations without reducing the inside diameter of the sheath. To this end and according to a first aspect, the invention concerns a device for transmitting a rotation movement, this device comprising a flexible shaft and a sheath inside which the shaft is housed, the sheath comprising a core formed by a hollow cylinder whose inside diameter is arranged so as to allow the rotation of the said shaft inside the said sheath. The core of the sheath comprises at least one zone forming a bearing which is obtained by plastic deformation of the core, this zone comprises at least three parts, two outer parts and a central part. These parts have axes substantially parallel to that of the core and have a diameter substantially equal to that of the core, the outer parts being substantially coaxial and with their axis offset with respect to the axes of the central part and the core.
According to one embodiment, the central part of the zone forming a bearing and the core of the sheath are substantially coaxial. According to one embodiment, the sheath comprises several zones forming a bearing spaced apart from each other by a distance of between 5 and 15 centimeters. According to another embodiment, the zones are disposed continuously along the sheath. According to one embodiment, the core of the sheath is provided on its internal surface with a flock coating.
According to a second aspect, the invention concerns an adjustment system for a motor vehicle, comprising at least one adjustment runner mounted on the structure of the vehicle and adjustable means of fixing the seat to the runner, the system also comprising a drive motor having at least one rotary output. The system also comprises a device for transmitting a rotation movement of the type described above which is disposed between the output of the said drive motor and the said fixing means, so as to move the fixing means along the adjustment runner in response to a rotation of the output. The invention will be clearly understood from a reading of the following description, given with reference to the accompanying figures.
A device for transmitting a rotation movement 1 comprises a flexible shaft 2 and a sheath 3. The shaft 2 is housed in the sheath 3, whose inside diameter is designed so as to allow the rotation of the shaft 2 in the sheath 3. The speeds of rotation of the shaft 2 are conventionally around 3000 revolutions/minute. To allow rotation at this speed, a clearance of a few tenths of a millimeter is provided between the shaft 2 and the sheath 3.
The sheath 3 comprises a core 4 and an external tubular envelope 5 enclosing the core 4. The core 4 can for example be formed by a helical spring made from metallic material. This spring is for example formed from a metallic strip wound in a helix. The turns of the spring are non-contiguous, which confers flexibility on the sheath. The external envelope 5 can be produced from an extruded plastics material.
Referring to FIGS. 1 and 2, the sheath 3 has a permanent deformation in the form of a zone forming a bearing 6, the bearing extending in the longitudinal direction of the device. The zone forming a bearing comprises three parts, two outer parts 7 and 8 and a central part 9. The axis of each of these parts is substantially parallel to that of the core 4. The outer parts 7 and 8 are also coaxial and their axis is offset with respect to that of the core 4. In the description, the axes are defined in the stable rectilinear position of the sheath, as depicted in FIGS. 1 and 2. Each part 7–9 also has an inside diameter substantially equal to the inside diameter of the core 4 and comprises a whole number of consecutive turns.
According to the embodiment of the invention depicted in FIG. 1, the zone forming a bearing 6 of the transmission device 1 comprises two outer parts 7, 8 and a central part 9 formed by a single turn. The axes of each part are offset with respect to the axis of the core so that the common axis of the outer parts 7 and 8 and the axis of the central part 9 are substantially symmetrical with respect to the axis of the core 4.
According to the embodiment of the invention depicted in FIG. 2, the zone forming a bearing 6 of the transmission device 1 comprises two outer parts 7, 8 formed by a single turn and a central part 9 formed by two turns. The central part 9 is also coaxial with the core 4 of the sheath. According to the invention, several zones forming a bearing can be distributed along the sheath. In one embodiment, the distance separating two zones is typically between 5 and 15 centimeters. According to another embodiment, the zones are disposed continuously along the sheath.
The zone forming a bearing 6 causes an offsetting of the metallic turns of the sheath 3 without reducing the inside diameter of the said turns. This creates a slightly sinuous path inside the sheath 3 with points of contact between the sheath 3 and the shaft 2 which are opposed with respect to the axis of the sheath and alternating on each side of this axis. These points of contact eliminate all possibility of vibrating the shaft in movement without for all that restricting the latter. The motor torque can thus be similar to that used with non-deformed sheaths and the sheath does not have a tendency to premature wear at the deformations. Moreover, the spaces left free between the sheath 3 and the flexible shaft 2 can form a reserve of grease 21 for lubricating the shaft 2.
The deformations of the sheath 3 are produced by plastic deformation of the sheath, for example by means of a press whose jaws are arranged so as to offset the turns radially. These deformations are therefore permanent and mounting the device requires no additional part for maintaining these deformations.
Referring to FIGS. 1 and 2 and according to a particular embodiment of the invention, the core 4 of the sheath 3 comprises a flock coating 10 on its internal surface, that is to say the surface facing the shaft 2. This is because it was possible to observe that such an arrangement in which the sheath is internally flock coated had optimum noise damping. The flock lining provides mechanical isolation between the shaft and the sheath. Forming this flock coating on the sheath, in combination with the deformation 6, gives good results from the acoustic point of view. The internal surface of the core 4 is covered by any known method, for example electrostatically, with a flock coating 10 which can comprise polyamide 6.6 fibres.
Such a device for transmitting a rotation movement can be used in a system for adjusting a motor vehicle seat 20 as depicted in FIG. 3. To this end, two runners 11 and 12 are fixed by any suitable means to the structure, not shown, of a motor vehicle. These runners have adjustment notches, the function of which will be described below. The runners 11 and 12 support the framework of a seat, also not shown, of the vehicle, whose movement and fixing with respect to the runners are provided by gears 13 and 14 respectively provided with toothed wheels cooperating with aforementioned notches on the runners 11 and 12.
An electric motor 15 is fixed to the structure of the vehicle or, in a variant, to the framework of the seat. This motor 15 has two rotary outputs 16 and 17. These outputs 16 and 17 are connected by devices for transmitting a rotation movement 1 according to the invention to the gears 13 and 14 respectively.